Avoiding_Action - because we (ATC) have no idea which configuration the aircraft is being flown in, and although the Mode S is displaying correctly, that does not mean the aircraft is going to that level. Secondly, sometimes different levels are set to get the aircraft moving - ie following late handover from the French, given a restriction FL130 level GWC, but then the Mode S reads FL80 for about 30 seconds before reading FL130. I was informed this just "gets the thing going down" as they knew it was a tight restriction.